I'm interested in data compression algorithms and file formats. In
particular, I like to reverse engineer proprietary, unknown file formats
and make decompressors which allow anyone to unpack these formats. My work
includes:

XAD clients and XFD
slaves:
XAD and XFD are both excellent Amiga decompression libraries. XFD handles
compressed executables and data files, XAD handles disk and file
archives. Between them, they handle thousands of compression formats. I
have written many decompressors for both libraries.

libmspack
is a library which intends to offer compressors and decompressors for the
following Microsoft file formats formats: CAB, CHM, HLP, LIT, SZDD and
KWAJ.

cabextract is a
popular UNIX program for decompressing Microsoft Cabinet
files. cabextract's decompression routines form the basis of the libmspack
CAB decompressor.

Convert .LIT is a program, written by an
anonymous author and hosted here, which allows people to decode Microsoft
eBook (LIT) files into their original HTML. Convert LIT's decompression
and decryption routines will form the basis of the libmspack LIT
decoder.

DeliDecrunch
is an XFD/XAD enabled drop-in
replacement for the standard DeliTracker Decrunch genie. It allows Amiga
users to play music straight from compressed files and archives. Because
it uses XFD and XAD, it supports hundreds more formats than the original
Decrunch genie.

ppcrack is a
portable program that decrypts or unpacks PowerPacker files, without
any need for a password. On a modern PC, it takes a couple of minutes.
ppcrack also comes with a tool called ppsimilar,
which will give you the correct decryption key immediately, should you
have an unencrypted PowerPacked file which "similar" enough to the
encrypted one. There is a set of benchmarking
and test files for people volunteering to port ppcrack to other
platforms.

Finally, some programs which don't fit in anywhere else:

ixadump extracts the files in an
iXalance demo, which is an OS independent demo loader system written by
The Black Lotus (TBL).

uncps unpacks .CPS files from many games,
including the SSI games "Eye of the Beholder" and "Eye of the Beholder
II", Westwood Studios' "Command and Conquer" and the Legend of Kyrandia
series.

uncpt unpacks Sinclair QL .CPT files,
created with the CPT tool written in 1989 by Sander Plomp. This is not the
Apple Macintosh "Compact" or "Compact Pro" format by Bill Goodman. The
original CPT and UNCPT tools came with these
instructions. You can find some CPT-encoded files here. Sander also wrote
an archiver called QARC, but I have not yet looked at that. For a start, I
can't find any QARC encoded files.